Movement assistance device

ABSTRACT

A apparatus includes an a exoskeleton system with a plurality of sensors for generating signals indicating a current motion and a current arrangement of at least the exoskeleton system, a hip segment, and at least one lower limb. The lower limb includes thigh and shank segments for coupling to a lateral surface of a user&#39;s leg. The thigh segment includes a first powered joint coupling the thigh segment to the hip segment, a second powered joint coupling the thigh segment to the shank segment, and a controller coupled to the sensors, the first powered joint, and the second powered joint. The controller is configured for determining a current state of the exoskeleton system and a current intent of the user based on the signals and generating control signals for the first and second powered joints based on the current state and the current intent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-provisional patentapplication Ser. No. 14/049,494, filed Oct. 9, 2013, which is acontinuation-in-part of U.S. National Stage application Ser. No.13/876,228, filed Mar. 27, 2013, which is a § 371 national stage entryof International Application No. PCT/US2011/053501, filed Sep. 27, 2011,which claims priority to U.S. Provisional Application No. 61/386,625,filed Sep. 27, 2010, the contents of all of which are herebyincorporated by reference. U.S. Non-provisional patent application Ser.No. 14/049,494, also claims priority to and the benefit of U.S.Provisional Application Ser. No. 61/711,286, filed Oct. 9, 2012, thecontents of which is herein incorporated by reference in its entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under NIH R01HD059832-01/05 awarded by National Institutes of Health. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to field of powered assistive devices, andmore specifically to powered assistive devices and methods.

BACKGROUND

There are currently about 262,000 spinal cord injured (SCI) individualsin the United States, with roughly 12,000 new injuries sustained eachyear at an average age of injury of 40.2 years. Of these, approximately44% (5300 cases per year) result in paraplegia. One of the mostsignificant impairments resulting from paraplegia is the loss ofmobility, particularly given the relatively young age at which suchinjuries occur. Surveys of users with paraplegia indicate that mobilityconcerns are among the most prevalent, and that chief among mobilitydesires is the ability to walk and stand. In addition to impairedmobility, the inability to stand and walk entails severe physiologicaleffects, including muscular atrophy, loss of bone mineral content,frequent skin breakdown problems, increased incidence of urinary tractinfection, muscle spasticity, impaired lymphatic and vascularcirculation, impaired digestive operation, and reduced respiratory andcardiovascular capacities.

In an effort to restore some degree of legged mobility to individualswith paraplegia, several lower limb orthoses have been developed. Thesimplest form of passive orthotics are long-leg braces that incorporatea pair of ankle-foot orthoses (AFOs) to provide support at the ankles,which are coupled with leg braces that lock the knee joints in fullextension. The hips are typically stabilized by the tension in theligaments and musculature on the anterior aspect of the pelvis. Sincealmost all energy for movement is provided by the upper body, these(passive) orthoses require considerable upper body strength and a highlevel of physical exertion, and provide very slow walking speeds. Thehip guidance orthosis (HGO), which is a variation on long-leg braces,incorporates hip joints that rigidly resist hip adduction and abduction,and rigid shoe plates that provide increased center of gravity elevationat toe-off, thus enabling a greater degree of forward progression perstride. Another variation on the long-leg orthosis, the reciprocatinggait orthosis (RGO), incorporates a kinematic constraint that links hipflexion of one leg with hip extension of the other, typically by meansof a push-pull cable assembly. As with other passive orthoses, the userleans forward against the stability aid while unweighting the swing legand utilizing gravity to provide hip extension of the stance leg. Sincemotion of the hip joints is reciprocally coupled through thereciprocating mechanism, the gravity-induced hip extension also providescontralateral hip flexion (of the swing leg), such that the stridelength of gait is increased. One variation on the RGO incorporates ahydraulic-circuit-based variable coupling between the left and right hipjoints. Experiments with this variation indicate improved hip kinematicswith the modulated hydraulic coupling.

In order to decrease the high level of exertion associated with passiveorthoses, the use of powered orthoses has been previously investigated,which incorporate actuators and an associated power supply to assistwith locomotion. More recently, a powered orthosis was developed bycombining three electric motors with an RGO, two of which are located atthe knee joints to enable knee flexion and extension during swing, andone of which assists the hip coupling, which in essence assists bothstance hip extension and contralateral swing hip flexion. The orthosiswas shown to increase gait speed and decrease compensatory motions,relative to walking without powered assistance.

In addition, control methods have been proposed for providing assistivemaneuvers (sit-to-stand, stand-to-sit, and walking) to paraplegicindividuals with the powered lower limb orthosis HAL, which is anemerging commercial device with six electric motors (i.e., poweredsagittal plane hip, knee, and ankle joints). Like the powered lower limborthosis HAL, two additional emerging commercial devices include theReWalk™ powered orthosis from Argo Medical Technologies and the eLEGS™powered orthosis from Berkeley Bionics. Both of these devices weredeveloped specifically for use with paraplegic individuals.

SUMMARY

Embodiments of the invention concern a movement assistance deviceembodied as a powered lower limb orthosis or exoskeleton that, like thedevices already mentioned, is intended to provide gait assistance toparaplegics by providing sagittal plane assistive torques at both hipand knee joints. An orthosis in accordance with the various embodimentsis different from conventional orthoses in the fact that it neitherincludes a portion that is worn over the shoulders, nor a portion thatis worn under the shoes. Also, an orthosis in accordance with thevarious embodiments has a significantly lower mass relative to therespective masses reported for other devices.

Additionally, orthoses in accordance with the various embodimentsincludes a new control architecture that enables a user to intuitivelyand autonomously control (i.e., without push-button controls or theassistance of a system operator) the basic movements associated withlegged mobility (i.e., sitting, standing, and walking). In particular, acontrol architecture is provided that enables a user to autonomouslynavigate through these movements, without the use of buttons or switchesor the aid of an external operator. Specifically, the controlarchitecture in accordance with the various embodiments enables the userto switch between sitting, standing, and walking, based on the user'supper body movement and the state of the orthosis.

The control architecture of the various embodiments also does notrequire any instrumentation under the foot, such as ground contactsensors or ground load sensors. Specifically, the controllerarchitecture strictly requires measurement of eight angles, all easilymeasurable by the lower limb exoskeleton. Based on these eight angles,the control method enables the user to intuitively and autonomouslycontrol (i.e., without push-button controls, without the assistance of asystem operator, and without instrumentation on the torso, arms,stability aid, or under the feet) the basic movements associated withlegged mobility (i.e., sitting, standing, walking, stopping, stairascent and descent). In some embodiments, the control architecture canalso function using a subset of these eight angles.

A powered limb prosthesis in accordance with the various embodiments canbe supplemented with functional electrical stimulation (FES) of theuser's muscles (i.e., using electrical stimulation to elicitcontractions of the user's muscles). The FES can be controlled toprovide as much movement as possible, with the remaining movementprovided by the assistance device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user using an orthosis in accordance with thevarious embodiments;

FIG. 2 shows a front view of the orthosis shown in FIG. 1;

FIG. 3 shows a side view of the orthosis shown in FIG. 1;

FIG. 4 shows an isometric view of the orthosis shown in FIG. 1;

FIG. 5A shows a partial cutaway view of a portion of the orthosis shownin FIG. 1;

FIG. 5B is a detailed exploded view of section B of FIG. 5A;

FIG. 6 is a functional diagram of an exemplary distributed embeddedsystem for an orthosis in accordance with the various embodiments;

FIG. 7 shows a state machine in accordance with the various embodimentsof the invention;

FIG. 8A is an X-Y plot of joint angle a function of the percent ofstride during a transition to a walking state;

FIG. 8B is an X-Y plot of joint angle a function of the percent ofstride during a transition between walking states;

FIG. 8C is an X-Y plot of joint angle a function of the percent ofstride during a transition to a standing state;

FIG. 9 is a schematic showing center of pressure during walking;

FIG. 10A is a schematic showing center of pressure during a transitionfrom sitting to standing;

FIG. 10B is a schematic showing center of pressure during a transitionfrom standing to sitting;

FIG. 11 shows one exemplary structure for a controller in accordancewith the various embodiments of the invention;

FIGS. 12A and 12B show angles in the sagittal and frontal planes,respectively, utilized for the operation for the controller of FIG. 11.

FIG. 13 is a schematic showing an exemplary arrangement for functionalelectrical stimulation in accordance with the various embodiments;

FIGS. 14 and 15 shows measured joint angle data for each of the joints,as a function of time, from 23 right steps and 23 left steps, overlaidonto the same plot;

FIG. 16 shows power use as a function of stride for the data in FIG. 13;

FIG. 17 shows joint angles (left and right hip, left and right knee) andstate, as a function of time, for a test subject.

FIG. 18A shows the system state for several steps (of slightly varyinglength), as a function of time;

FIG. 18B shows the estimated CoP (Xc) (solid line) and the CoP switchingthreshold (Xĉ) (dashed line) for the same steps as in FIG. 18A;

FIG. 18C shows the estimate of step length (Xh) for the same steps inFIGS. 18A and 18B;

FIGS. 19A, 19B, and 19C presents the sequences of finite statescorresponding to each of first, second, and third TUG tests,respectively;

FIG. 20 graphically shows the results of TUG heart rate and TMWT heartrate for a subject using various walking methods.

FIG. 21 graphically shows TUG heart rate % change, TMWT heart rate %change, and Borg perceived exertion for a subject using various walkingmethods

DETAILED DESCRIPTION

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the instantinvention. Several aspects of the invention are described below withreference to example applications for illustration. It should beunderstood that numerous specific details, relationships, and methodsare set forth to provide a full understanding of the invention. Onehaving ordinary skill in the relevant art, however, will readilyrecognize that the invention can be practiced without one or more of thespecific details or with other methods. In other instances, well-knownstructures or operations are not shown in detail to avoid obscuring theinvention. The present invention is not limited by the illustratedordering of acts or events, as some acts may occur in different ordersand/or concurrently with other acts or events. Furthermore, not allillustrated acts or events are required to implement a methodology inaccordance with the present invention.

1. POWERED ORTHOSIS CONFIGURATION

Although the various embodiments will be discussed at times with respectto orthoses for providing mobility assistance for users with paraplegia,the various embodiments are not limited in this regard. The variousembodiments are equally application to other applications. For example,these can include mobility assistance for users with other conditionsother than paraplegia, rehabilitation and mobility assistance forstroke-impaired users, and mobility assistance for users withneuromuscular disabilities that impair legged mobility, to name a few,including human and non-human users. Thus, the various embodiments canbe applied to any applications in which mobility assistance orenhancement is needed, either permanently or temporarily.

Further, although the various embodiments will be generally describedwith respect to the exemplary orthosis described below, the variousembodiments are not limited to this particular configuration. Thevarious embodiments can be embodied in or used with any type ofexoskeleton system, such as the orthosis described below.

The term “exoskeleton system”, as used herein, refers to any type ofdevice that can be worn or otherwise attached to a user, where thedevice is configured to provide energy for motion of the one or moreportions of the user.

An exemplary powered lower limb orthosis 100 in accordance with thevarious embodiments is shown in FIGS. 1-4. Specifically, the orthosis100 shown in FIGS. 1-4 incorporates four motors, which impose sagittalplane torques at each hip joint 102R, 102L and knee joint 104R, 104L.The orthosis 100 can be used with a stability aid 103, such as crutches,a walker, or the like.

As seen in the figure, the orthosis contains five segments, which are:two shank segments 106R and 106L, two thigh segments 108R and 108L, andone hip segment 110. Each of thigh segments 108R and 108L includes athigh segment housing 109R and 109L, respectively, and link or connector112R and 112L, respectively, extending from each of the knee joints 104Rand 104L and configured for moving in accordance with the operation ofthe knee joints 104R and 104L to provide sagittal plane torque at theknee joints 104R and 104L. The connectors 112R and 112L are furtherconfigured for mechanically coupling each of thigh segments 108R and108L to respective ones of the shank segments 106R and 106L. Further,each of thigh segments 108R and 108L also includes a link or connector114R and 114L, respectively, extending from each of the hip joints 102Rand 102L and moving accordance with the operation of the hip joints 102Rand 102L to provide sagittal plane torque at the knee joints 104R and104L. The connectors 114R and 114L are further configured formechanically coupling each of thigh segments 108R and 108L to the hipsegment 110.

As show in FIG. 1, the orthosis 100 can be worn by a user. To attach theorthosis to the user, the orthosis 100 can include fastening points 101for attachment of the orthosis to the user via belts, loops, straps, orthe like. Further, for comfort of the user, the orthosis 100 can includepadding (not shown) disposed along any surface likely to come intocontact with the user.

In some embodiments, the various components of orthosis 100 can bedimensioned for the user. However, in other embodiments, the componentcan be configured to accommodate a variety of users. For example, insome embodiments, one or more extension elements can be disposed betweenthe shank segments 106R and 106L and the thigh segments 108R and 108L toaccommodate users with longer limbs. In other configurations, thelengths of the two shank segments 106R and 106L, two thigh segments 108Rand 108L, and one hip segment 110 can be adjustable. That is, thighsegment housings 109R, 109L, the shank segment housings 107R and 107Lfor the shank segments 106R, 106L, respectively, and the hip segmenthousing 113 for the hip segment 110 can be configured to allow the useror prosthestist to adjust the length of these components in the field.For example, these components can consist of slidable or movablesections that can be held in one or more positions using screws, clips,or any other types of fasteners. In view of the foregoing, the two shanksegments 106R and 106L, two thigh segments 108R and 108L, and one hipsegment 110 can form a modular system allowing for one or more of thecomponents of the orthosis 100 to be selectively replaced and forallowing an orthosis to be created for a user without requiringcustomized components. Such modularity can also greatly facilitate theprocedure for donning and doffing the device.

In orthosis 100, disposed within each of thigh segment housings 109R,109L includes substantially all the components for operatingcorresponding ones of the knee joints 104R, 104L and the hip joints102R, 102L. In particular, each of thigh segment housings 109R, 109Lincludes two motors which are used to drive the hip and kneearticulations. However, the various embodiments are not limited in thisregard and some components can be located in the hip segment 110 and/orthe shank segments 106R, 106L. For example, a battery 111 for theorthosis can be located within in hip segment housing 113 and connectors114R and 114L can also provide means for connecting the battery 111 toany components within either of thigh segments 108R and 108L. Forexample, the connectors 114R and 114L can include wires, contacts, orany other types of electrical elements for electrically connectingbattery 111 to electrically powered components in thigh segments 108Rand 108L. In the various embodiments, the placement of battery 111 isnot limited to being within hip segment housing 113. Rather, the batterycan be one or more batteries located within any of the segments oforthosis 100.

In the various embodiments, in order to maintain a low weight fororthosis and a reduced profile for the various components, asubstantially planar drive system is used to drive the hip and kneearticulations. For example, each motor can each drive an associatedjoint through a speed-reduction transmission using an arrangement ofsprocket gears and chains substantially parallel to the plane ofsagittal motion. One exemplary configuration for such an arrangement ofa motor is illustrated in FIG. 5A. Using the configuration in FIG. 5A,it is possible to achieve a low profile orthosis, adding less than 5 cmat the hip and thigh sections.

For example, in one embodiment, the profile of the orthosis in thefrontal plane can be configured so as to add 3.2 cm at the hip and kneejoint, and 4.8 cm at mid-thigh, such that a user is able to sit in aconventional armchair or wheelchair. Similarly, the hip segmentprotrudes approximately 3.2 cm posteriorly from the user's lower back,such that it should not significantly interfere with a seat back. Theorthosis does not extend above mid-abdomen and requires nothing to beworn over the shoulders and nothing above the lower back, whichpresumably renders the device less noticeable when sitting at a desk ortable. The compact design of the orthosis is greatly facilitated by theintegration of the distributed embedded system within the orthosisstructure.

In the various embodiments, the orthosis 100 is not configured forweight bearing. That is, as shown in FIG. 1, the orthosis 100 will notinclude feet or other weight bearing structures. Rather, as shown inFIG. 1, the orthosis 100 is configured so that the combined lenth of theshank segments 106R and 106L and the corresponding one of the thighsegments 108R and 108L is less than a length of the leg of the user.This results in an orthosis with potential health benefits for the user.In particular, the ability to stand and walk can reverse or reduce theamount of physiological impairments typically associated withimmobility, including muscular atrophy, loss of bone mineral content,frequent skin breakdown problems, increased incidence of urinary tractinfection, muscle spasticity, impaired lymphatic and vascularcirculation, impaired digestive operation, and reduced respiratory andcardiovascular capacities.

Although FIG. 5A will be described with respect to the operation of kneejoint 104R, this is for ease of illustration. That is, the other jointscan be configured to operate in a substantially similar manner. FIG. 5Ais a cutaway view of orthosis 100 around knee joint 104R illustratingone exemplary configuration for a motor 502 driving knee joint 102R inan orthosis in accordance with the various embodiments. As shown in FIG.5A, the knee joint 102R can be implemented by disposing a joint sprocketgear 504 at one end of thigh segment housing 109R parallel to thesagittal plane and configuring the joint sprocket gear 504 to rotateparallel to the sagittal plane. To provide the sagittal plane torque forknee joint 102R, the connector 112R can extend from the joint sprocketgear 504 and be mechanically connected, so that rotation of the jointsprocket gear 504 results application of torque to the shank segment106. As shown in FIG. 5A, a slot or receiving element 506 can beprovided for the connector 112R to link the thigh segment 108R and shanksegment 106R. The receiving element 506 and the connector 112R can beconfigured such that the connector can removably connect the thighsegment 108R and shank segment 106R. In the various embodiments, clips,screws, or any other types of fastener arrangements can be used toprovide a permanent or a removable connection. In some embodiments,quick connect or “snap-in” devices can be provided for providing theconnection. That is, these quick connect devices allow connections to bemade without the need of tools. These types of quick connect devices cannot only be used for mechanically coupling, but for electrical coupling.In some embodiments, a single quick connect device can be used toprovide both electrical and mechanical coupling. However, the variousembodiments are not limited in this regard and separate quick connectdevices can be provided for the electrical and mechanical coupling. Itis worth noting that with quick disconnect devices at each joint, theorthosis can be easily separated into three modular components—rightleg, left leg, and hip segment—for ease of donning and doffing and alsofor increased portability.

A detailed view of an exemplary quick-connect configuration is shown inFIG. 5B. FIG. 5B is a detailed view of section “B” of FIG. 5A. As shownin FIG. 5B, the connector 112R is a member that extends from thighsegment 108R. The connector 112R is configured to slide into receivingelement 506. The connector 112R can then be mechanically locked intoplace via the combination of a latch 526 on shank segment 106R and acatch 528 on connector 112R.

As noted above, the connectors 112R, 112L, 114R, and 114L can beconfigured to provide mechanical and electrical connections. Referringback to FIG. 5B, in the event that an electrical connection is neededbetween the thigh segment 108R and shank segment 106R, wires can berouted through the interior of connector 112R to electrical contacts530. A corresponding set of electrical contacts (not shown) would alsobe provided in the interior of receiving element 506. Accordingly, whenconnector 112R is locked into receiving element 506, the electricalcontacts 530 are placed in contact with the electrical contacts withinreceiving element 506. A similar configuration can be provided for links112L, 114R, and 114L. It is noted though that the various embodimentsare not limited to solely the catch and latch combination of FIG. 5B.Rather any other type of fastening or locking mechanism can be usedwithout limitation.

Referring back to FIG. 5A, the knee joint 104R is actuated via operationof motor 502, as discussed above. The motor 502 can be an electric motorthat drives the knee joint 104R (i.e., joint sprocket gear 504) using atwo-stage chain drive transmission. For example, as shown in FIG. 5A, afirst stage can consist of the motor 502 driving, either directly or viaa first chain 512, a first drive sprocket gear 514. The first drivesprocket gear 514 is mechanically coupled to a second drive sprocketgear 516 so that they rotate together about the same axis based on thepower applied by motor 502 to first drive sprocket gear 514. The seconddrive sprocket gear 516 can be arranged so that it is disposed in thesame plane as the joint gear 504. Thus, a second chain 518 can then beused to drive joint sprocket gear 504 using the second drive sprocketgear 516 and actuate the knee joint 104R. The gear ratios for thevarious components described above can be selected based on a neededamount of torque for a joint, power constraints, and space constraints.

Each stage of the chain drive transmission can include tensioners, whichcan remove slack from a chain and mitigate shock loading. Suchtensioners can be adjustable or spring loaded. For example, as shown inFIG. 5A, spring loaded tensioners 508 and 510 are shown for second chain518. Similarly, tensioners 509 and 511 can also be provided for firstchain 512 (if present).

In addition, a brake can be provided for motor 502. For example, asshown in FIG. 5, a solenoid brake 520 is provided which engages a brakepad 522 against the rotor 524 of the motor 502 in one state, anddisengages the brake pad 522 in another state. However, the variousembodiments are not limited to this particular brake arrangement and anyother methods for providing a brake for motor 502 can be used withoutlimitation.

The configuration illustrated in FIG. 5A has been discussed above withrespect to an arrangement of sprocket gears and chains. However, thevarious embodiments are not limited in this regard. That is, any otherarrangement of gears, with or without chains, and providing a reducedprofile can be used. Further, the various embodiments are not limited toan arrangement of gears and/or chains For example, in someconfigurations, a belt and pulley arrangement could be used in place ofthe chain and sprocket arrangement. Further, a friction drivearrangement can also be used. Also, any combination of the arrangementsdiscussed above can be used as well. Additionally, different joints canemploy different arrangements.

In the various embodiments, a motor for each of joints 102R, 102L, 104R,104L can be configured to provide a baseline amount of continuous torqueand a higher amount of torque for shorter periods of time. For example,in one configuration, at least 10 Nm of continuous torque and at least25 Nm of torque for shorter (i.e., 2-sec) durations are provided. Inanother example, up to 12 Nm of continuous torque and 40 Nm of torquefor shorter (i.e., 2-sec) durations. As a safety measure, both kneejoints 104R and 104L can include normally locked brakes, as discussedabove, in order to preclude knee buckling in the event of a powerfailure.

It is worth noting that an orthosis in accordance with the variousembodiments does not contain foot or ankle components. However, anorthosis in accordance with the various embodiments can be configured tobe used in conjunction with a standard ankle foot orthosis (AFO) 115 toprovide stability for the ankle and/or to preclude foot drop during theswing phase of gait.

In the orthosis 100, control of the various joints is provided using apair of embedded control systems 116R and 116L embedded in one of thighsegments 108R and 108L, respectively. The embedded control systems 116Rand 116L can be used to define a distributed embedded system (DES) toprovide cooperative operation between thigh segments 108R and 108L. Theembedded control systems 116R and 116L are shown in FIGS. 3 and 4 usingdashed lines to indicate they are concealed by other features in thesefigures.

A functional diagram of an exemplary DES 600 formed using the embeddedcontrol systems 116R and 116L is given in FIG. 6. The DES 600 is poweredby battery 111, such as a 29.6 V, 3.9 A·hr lithium polymer battery. TheDES 600 can include includes a power management module 602, acomputation or data processing module 604, electronic signalconditioning and sensor interface module 606, power electronics 608, andcommunication electronics 610 to interface components within the DES 600and between the DES 600 and a host computer. To form the DES 600 theembedded control systems 116R and 116L can be communicatively coupledvia wired communications links in the hip segment 110 or wirelesscommunications links between the embedded control systems 116R and 116L.The can include any type of wireless communications links. For example,these can include wireless communication links according to any of theIEEE 802.xx standards, Bluetooth™, and any derivations thereof. However,the various embodiments are not limited in this regard and any othertypes of wireless communication links can be used.

The power management module 602 provides, from the battery 111 canprovide signal conditioning and regulation. Additionally, the powermanagement modules For example, the power management module 602 isconfigured to provide linearly regulated ±12 and +3.3 V, which are usedfor signal conditioning and computation, and are derived fromintermediate ±12.5 and +5 V switching regulators for efficientconversion. In some embodiments, the orthosis 100 can include a visualdisplay, controlled by the power management module 602, to indicate astate of the battery. The visual display can be alphanumeric or symbolic(e.g., one or more lights to indicate battery status).

The computation module 604 consists of microcontroller units within eachof embedded control systems 116R and 116L. For example, as shown in FIG.6, the microcontroller units can be s 80 MHz PIC32 microcontrollers,each with 512 kB flash memory and 32 kB RAM, and each of which consumeapproximately 400 mW of power. These microcontrollers can be programmed.For example, the programming can be performed in C programming languageusing MPLAB IDE and the MP32 C Compiler (both from Microchip Technology,Inc.). However, the various embodiments are not limited in this regardand any other types of programming methods can be used.

In operation, the computation module 604 (i.e., the twomicrocontrollers) drive the motors associated with each of joints 102R,102L, 104R, and 104L using servodrivers or servoamplifiers in the powerelectronics 608, such as four-quadrant switching servoamplifiers orpulse-width-modulated (PWM) power transistor drivers. The computationmodule 604 also drives the knee brakes via pulse-width-modulated (PWM)power transistors in the power electronics 608.

The computation module 604 is configured in the various embodiments todrive the motors associated with each of joints 102R, 102L, 104R, and104L based, at least in part, on sensor data regarding the state of theorthosis 100, as further discussed below. Accordingly, the sensorinterface module 606 can be configured to provide and/or providecommunications with sensors dispose in orthosis 100. In someembodiments, all of the sensors can be disposed within one of thighsegments 108R and 108L. For example, these sensors can be embeddedwithin each of embedded control systems 116R and 116L. In oneconfiguration of orthosis 100, physical sensing consists ofHall-effect-based angle and angular velocity sensing in each hip joint104R, 104L and each knee joint 102R, 102L, and 3-axis accelerometers andsingle-axis gyroscopes disposed elsewhere in each of thigh segments 108Rand 108L.

Although the description above describes a symmetric arrangement ofcomponents in for each of embedded control systems 116R and 116L, thevarious embodiments are not limited in this regard. In otherembodiments, one or more of the module described above may be locatedwithin one of embedded control systems 116R and 116L.

In some embodiments, the orthosis 100 can be configured to operatecooperatively with sensors embedded in the stability aid 103. The DEScan be configured to communicate with such sensors via wireline orwireless communications links, as described above.

2. POWERED ORTHOSIS CONTROL ARCHITECTURE

2.1 Joint-Level Controllers

The general control structure of an orthosis in accordance with thevarious embodiments consists of variable-impedance joint-levelcontrollers, the behavior of which is supervised by an event-drivenfinite-state controller. The joint-level controllers consist ofvariable-gain proportional-derivate (PD) feedback controllers aroundeach (hip and knee) joint, where at any given time, the control inputsinto each controller consists of the joint angle reference, in additionto the proportional and derivative gains of the feedback controller.Note that the latter are constrained to positive values, in order toensure stability of the feedback controllers. With this controlstructure, in combination with the open-loop low output impedance of theorthosis joints, the joints can either be controlled in a high-impedancetrajectory tracking mode, or in a (relatively) low-impedance mode, byemulating physical spring-damper couples at each joint. The former isused where it may be desirable to enforce a predetermined trajectory(e.g., during the swing phase of gait), while the latter is used when itmay be preferable not to enforce a pre-determined joint trajectory, butrather to provide assistive torques that facilitate movement toward agiven joint equilibrium point (as in transitioning from sitting tostanding), or to impose dissipative behavior at the joint (as intransitioning from standing to sitting).

2.2 Finite-State Control Structure

The following section describes one exemplary embodiment of a controlstructure that enables the autonomous control of standing, walking, andsitting. However, this particular control structure is provided solelyfor ease of illustration of the various embodiments. In the variousembodiments, the control structure can include additional activitymodes, which would be implemented in a similar manner. These can includeupslope and downslope walking, stair ascent and descent, and curb ascentand descent, to name a few. It is worth noting that curb ascent anddescent can also be a subset of the stair ascent and descentfunctionality.

The joint-level controller receives trajectory commands, as well as PDgains, from a supervisory finite-state machine (FSM) 700, which (forsitting, standing, and walking) consists of 12 states, as shown in FIG.7. The FSM 700 consists of two types of states: static states andtransition states. The static states consist of sitting (S1), standing(S2), right-leg-forward (RLF) double support (S3), and left-leg-forward(LLF) double support (S4). The remaining 8 states, which transitionbetween the four static states, include sit-to-stand (S5), stand-to-sit(S6), stand-to-walk with right half step (S7), stand-to-walk with lefthalf step (S11), walk-to-stand with left half step (S10), walk-to-standwith right half step (S12), right step (S9), and left step (S8).

Each state in the FSM 700 is fully defined by the combination of a setof trajectories, and a set of joint feedback gains. In general, thelatter are either high or low. The set of trajectories utilized in sixof the eight transition states are shown in FIGS. 8A-8C. FIG. 8A is anX-Y plot of joint angle a function of the percent of stride during atransition to a walking state (S7, S11 in FIG. 7). Curves 802 are curvesfor swing of the hip and knee, represented by dashed and solid lines,respectively. Curves 804 are curves for stance of the hip and knee,represented by dashed and solid lines, respectively. FIG. 8B is an X-Yplot of joint angle a function of the percent of stride during atransition between walking states (S8, S9 in FIG. 7). Curves 806 arecurves for swing of the hip and knee, represented by dashed and solidlines, respectively. Curves 808 are curves for stance of the hip andknee, represented by dashed and solid lines, respectively. FIG. 8C is anX-Y plot of joint angle a function of the percent of stride during atransition to a standing state (S10, S12 in FIG. 7). Curves 810 arecurves for swing of the hip and knee, represented by dashed and solidlines, respectively. Curves 812 are curves for stance of the hip andknee, represented by dashed and solid lines, respectively.

For all the trajectories shown in FIGS. 8A-8C, the joint feedback gainsare set high. The final angles of the trajectories shown in FIGS. 8A-8Cfor the various joints define the constant joint angles that correspondto the static states of RLF double support (S3), LLF double support(S4), and standing (S2). Three states remain, which are the static stateof sitting (S1) and the two transition states of sit-to-stand (S5) andstand-to-sit (S6). The static state of sitting (S1) is defined by zerogains, and therefore the joint angles are unimportant. The transitionfrom stand-to-sit (S6) consists of a zero proportional gain and a highderivate gain (i.e., damping without stiffness). Thus, the joint anglesare also immaterial for this state, assuming they are constant. Finally,the sit-to-stand (S5) state is defined by standing (S2) joint angles,and utilizes a set of PD gains that ramp up from zero to a value thatcorresponds to a high impedance state. Together, Table I and FIGS. 8A-8Csummarize the trajectories and nature of the feedback gains thattogether define completely the behavior in all states of the FSM shownin FIG. 7.

TABLE 1 Joint controller characteristics within each state. State TypeGains Control Priority S1- Sitting Static Low NA S2- Standing StaticHigh Position S3- Right Forward Static High Position S4- Left ForwardStatic High Position S5- 1 to 2 Transition N.A Gain S6- 2 to 1Transition N.A Gain S7- 2 to 3 Transition High Trajectory S8- 3 to 4Transition High Trajectory S9- 4 to 3 Transition High Trajectory S10- 3to 2 Transition High Trajectory S11- 2 to 4 Transition High TrajectoryS12- 4 to 2 Transition High Trajectory

2.3 Switching Between States

The volitional command of the basic movements in the FSM is based on thelocation of the (estimated) center of pressure (CoP), defined for the(assumed quasistatic user/orthosis) system as the center of massprojection onto the (assumed horizontal) ground plane. This notion isillustrated in FIG. 9, which is a schematic for illustrating how todetermine the approximate location of the CoP, relative to theforward-most heel. It is assumed that, with the use of the stabilityaid, the user can affect the posture of his or her upper body, and thuscan affect the location of the CoP. By utilizing the accelerometers inthe orthosis, which provide a measure of the thigh segment angle (a inFIG. 9) relative to the inertial reference frame (i.e., relative to thegravity vector), in combination with the joint angle sensors (whichprovide a measure of the configuration of the orthosis and user), theorthosis controller can estimate the location of the CoP (in thesagittal plane). More specifically, in this estimation, the authorsassume level ground; that the heels remain on the ground; that the head,arms, and trunk (HAT) can be represented as a single segment with fixedinertial properties; and that out-of-sagittal-plane motion is small.Given these assumptions, along with estimates of the length, mass andlocation of center of mass of each segment (right and left shank, rightand left thigh, and HAT), the controller can estimate the projection ofthe CoP on the ground. Let the distance from the forward-most heel tothe CoP be X_(c), where a positive value indicates that the CoP liesanterior to the heel, and a negative number indicates the CoP liesposterior to the heel (see FIG. 9).

From a state of double support (S3 or S4), the user commands the nextstep by moving the CoP forward, until it meets a prescribed threshold,at which point the FSM will enter either the right step or left stepstates, depending on which foot started forward.

From a standing position (S2), the user commands a step by similarlymoving the CoP forward until it meets a prescribed threshold, but alsoleaning to one side in the frontal plane (as indicated by the 3-axisaccelerometers in the thigh segments), which indicates that the orthosisshould step with the leg opposite the direction of frontal plane lean(i.e., step forward with the presumably unweighted leg). That is,leaning to the right (and moving the CoP forward) will initiate a leftstep, while leaning to the left (and moving the CoP forward) willinitiate a right step.

The transitions between standing (S2) and sitting (S1) states areillustrated in the schematics show in FIGS. 10A and 10B. To transitionfrom a sitting to a standing state (S1 to S2), the user leans forward asillustrated in FIG. 10A, which shifts the CoP forward to a predeterminedthreshold, which initiates the transition from sitting to standing. Notethat FIG. 10A shows the case where the user's CoP is not sufficientlyforward to initiate a transition from sitting to standing. In order totransition from a standing state (S2) to a sitting state (S1), the usershifts the CoP rearward, such that the CoP lies behind the user, asshown in FIG. 10B

Finally the transition from (either case of) double support to standing(i.e., from either S3 or S4, to S2) is based on the timing associatedwith crossing the CoP threshold. That is, if the CoP does not cross theCoP threshold within a given time following heel strike (i.e., if thecontroller remains in either state S3 or S4 for a given duration),subsequent crossing of the CoP threshold will transition to standing(S2) rather than to the corresponding double support configuration. Thatis, a sufficient pause during gait indicates to the system that the userwishes to stand, rather than continue walking forward. A summary of allswitching conditions, governing the user interface with the FSMcontroller, is given in Table 2.

TABLE 2 Finite state controller switching conditions STATE MACHINESWITCHING CONDITIONS Transition Condition S1 to S5 The user leansforward and pushes up. S5 to S2 Hip and knee joints meet the Standing(S2) configuration. S2 to S7 The user leans forward and left. S7 to S3Hip and knee joints meet the Right Forward (S3) configuration. S3 to S8The user leans forward. S8 to S4 Hip and knee joints meet the LeftForward (S4) configuration. S4 to S9 The user leans forward. S9 to S3Hip and knee joints meet the Right Forward (S3) configuration.  S3 toS10 The user pauses for a predetermined period prior to leaning forward.S10 to S2  Hip and knee joints meet the Standing (S2) configuration. S2to S6 The user leans backward. S6 to S1 A predetermined time has lapsed. S2 to S11 The user leans forward and right. S11 to S4  Hip and kneejoints meet the Left Forward (S4) configuration.  S4 to S12 The userpauses for a predetermined period prior to leaning forward. S12 to S2 Hip and knee joints meet the Standing (S2) configuration.

The previous discussion indicates that the user-initiated right and leftsteps occur when the estimated location of the CoP (relative to theforward heel) exceeds a given threshold. The authors have found thatthis approach provides enhanced robustness when this threshold is afunction of the step length. That is, despite high-gain trajectorycontrol in the joints of the orthosis during swing phase, scuffing ofthe foot on the ground, as occasionally occurs, in combination withcompliance in the orthosis structure, can alter the step length duringwalking. In the case of a small step length, the forward thigh is nearlyvertical, and the user is more easily able to move the CoP forward ofthe forward heel. In the case of a large step length, the forward thighis forms a larger angle with the vertical, and moving the CoP forward ismore difficult. As such, the CoP threshold during walking wasconstructed as a linear function, where the CoP threshold (i.e., theamount the CoP must lie ahead of the forward heel) decreases withincreasing step size.

In the various embodiments, any sensors located within a stability aidcan be used to provide additional data for determining COP or a currentstate within the state machine.

In some embodiments, one or more acoustic transducers can be embeddedwithin one or more portions of the orthosis (such as within either ofhousings 109R and 109L). In such embodiments, the acoustic transducercan be configured to generate acoustic signals (i.e., vibrations)indicating a change in state. For example, the transducer can beoperated to provide specific patterns of vibration or sound for eachstate or transition. In other embodiments, the motors used to actuatethe hip or knee joints can be used as the transducer for emitting soundor vibration. In still other embodiments, visual indicia of the state ortransition can be provided. That is, a display or lights can be providedto indicate the state or transition. For example, in embodimentsincluding a display or lights indicating a battery state, the display orlights can also be configured to visually indicate the state ortransition. In still other embodiments, audio indicia of the state ortransition can be provided. That is, one or more sounds can be providedto indicate the state or transition. In yet other embodiments, tactileindicia of the state or transition can be provided. That is, theorthosis can include devices which adjustable features so that the stateor transition can be communicated to the user via touch,

The control methodology above has been described with respect to anorthosis including thigh and shank segments for both legs of the user.However, the various embodiments are not limited in this regard. In someembodiments, an orthosis can be configured to assist movement of a firstleg of a user and allow the user to move a second, sound leg withoutassistance. In these embodiments, sensors can be positioned to detectthe motion of the sound leg and the DES can then determine controlsignals for the first leg. For example, the user can wear a covering onthe sound leg, such as a garment or a splint, which includes thesesensors.

2.4 Exemplary Configuration for the Finite-State Control Structure

The control structure described above can be implemented in a variety ofways. However, for ease of illustration and greater understanding of thevarious embodiments, an exemplary implementation a control structure inaccordance with the various embodiments will now be discussed.

The exemplary control method incorporates a finite state structure asillustrated in FIG. 11. In particular, the method switches between thestates shown in FIG. 11 utilizing measurement of the exoskeletonconfiguration as defined in FIGS. 12A and 12B. Specifically, measurementof the exoskeleton configuration, as described here, includesmeasurement of eight angles, which include the knee and hip angles ofthe exoskeleton (i.e., the angles θ_(rh), θ_(rk), θ_(lh), and θ_(lk) inFIG. 12A), in addition to measurement of the right and left thigh anglesrelative to the vertical (i.e., relative to the gravity vector g). Thelatter includes the angles with respect to the vertical in the sagittalplane (i.e., x-y plane in FIG. 12A) of the left and right thigh segments(the angles α_(r) and α_(l) in FIG. 12A), and the angles with respect tothe vertical in the frontal plane (i.e., y-z plane in FIG. 12B) of theleft and right thigh segments (the angles γ_(r) and γ_(l) in FIG. 12B).

2.4.1 Walking

As depicted in FIG. 11, the exemplary walking controller consists of atleast a right stepping motion (right step) and a left stepping motion(left step), generally separated by a double-support phase (both feet onthe ground), in which either the right or left foot, respectively, isforward. In the proposed method, the user indicates intent to take thenext step (i.e., to trigger a right or left stepping motion) based onthe angle with respect to the vertical in the sagittal plane of theforward thigh (i.e., α of the forward leg) exceeding a predeterminedthreshold (where moving the forward thigh in the clockwise direction, asshown in the figure, will trigger a subsequent step of the oppositeleg). This can be referred to as “thigh tilt” in the sagittal plane. Theuser can affect the thigh tilt via use of his or her stability aid(e.g., forearm crutches or walker). The step triggering threshold canfurther be a function of the size of the previous step, as indicated forexample by the difference between the right and left hip angles in thedouble support phase, or the difference between the right and left thighangles.

For example, in the case the previous step was small (i.e., the feet arerelatively close together), the next step may be triggered by a largerthigh tilt (i.e., more clockwise movement of the forward thigh in thex-y plane in FIG. 12A). In the case the previous step was large (i.e.,the feet are relatively far apart), the next step may be triggered by asmaller thigh tilt (i.e., less clockwise movement of the forward thigh).In another embodiment, the next step can be triggered by a change inthigh tilt, relative to, for example, the initial thigh tilt whenentering the current double-support state. The sagittal plane thighthreshold for triggering the next step may also be inversely related tothe angular velocity of the thigh in the sagittal plane, such that alarger angular velocity might reduce the tilt threshold (i.e., a largerangular velocity in the clockwise direction will require a smallermovement in the clockwise direction), while a smaller angular velocitymight increase the threshold.

2.4.2 Transitions Between Walking and Standing

As depicted in FIG. 11, the exoskeleton controller consists of at leasta standing state (i.e., right and left feet are essentially aligned inthe sagittal plane) and at least one stepping state. In a preferredembodiment of the walking controller, the user must meet the previouslydescribed condition (on the sagittal plane thigh tilt) within apredetermined period of time in order to trigger the subsequent steppingstate. In this embodiment of the walking controller, if the user doesnot trigger the subsequent stepping state within a predetermined periodof time, the subsequent step (when triggered) will return theexoskeleton to the standing configuration (i.e., the next step willeffectively be a half step rather than a full step, returning theexoskeleton to the standing state). In a preferred embodiment, the userreceives a vibratory feedback for a short duration, when the period oftime required to take the next full step has elapsed. This vibratoryfeedback informs the user that triggering the next step will be a halfstep that will return the user to the standing state. In a preferredembodiment, the half step motion is noticeably slower than the full stepmotion, which informs the user that the step is a half step.

In order to return to the stepping state from the standing state, theuser can exceed a predetermined thigh tilt. Since the feet are together,the thigh tilt threshold can for example be based on the sagittal planethigh tilt of a single leg, or the average thigh tilt of both legs.Further, in a preferred embodiment, the user must meet this tiltthreshold for a predetermined period of time in order to enter the(right or left) stepping state. In one embodiment of the controller, thefirst step from the standing state is always either a right step or aleft step. In another embodiment, the user can combine sagittal planethigh tilt (α's in FIG. 12A) with frontal plane thigh tilt (γ's in FIG.12B), in order to determine which leg (right or left) will step first.For example, if a user meets a predetermined thigh tilt threshold in thesagittal plane, and also meets a predetermined thigh tilt in the frontalplane, the exoskeleton will enter a step with the leg that the user is“leaning” away from in the frontal plane (i.e., a frontal plane thightilt towards the right will trigger a left step, while a frontal planethigh tilt towards the left will trigger a right step). In a preferredembodiment, the exoskeleton will generate a vibratory feedback to theuser (i.e., will generate a vibration in the exoskeleton) when the userhas met the threshold condition to enter the left or right steppingstate. In a preferred embodiment, this vibratory feedback will continueuntil the predetermined period of time has lapsed and the step istriggered, or until the user no longer meets the threshold condition.This implementation notifies the user (with vibration) when he or shehas met the condition to take a step, and provides a period of time inwhich the user can correct the thigh configuration, should he or she notwant to trigger a step (i.e., not want to start walking).

2.4.3 Transitions Between Standing and Sitting

As depicted in FIG. 11, the exoskeleton controller consists of at leasta sitting state and a standing state. In order to enter the sittingstate from the standing state, the user can exceed a predeterminedsagittal plane thigh tilt in the posterior direction (orcounterclockwise direction in the sagittal plane in FIG. 12A). The thightilt can (for example) be based on the average sagittal plane thigh tiltof both legs. In a preferred embodiment, the user must meet this tiltthreshold for a predetermined period of time in order to enter thesitting state. In a preferred embodiment, the exoskeleton will generatea vibratory feedback to the user (i.e., will generate a vibration in theexoskeleton) when the user has met the threshold condition to enter thesitting state. In a preferred embodiment, this vibratory feedback willcontinue until the predetermined period of time has lapsed andtransition to the sitting state is triggered, or until the user nolonger meets the threshold condition for sitting. This implementationnotifies the user (with vibration) when he or she has met the conditionto sit, and provides a period of time in which the user can correct thethigh configuration, should he or she not want to sit. Additionally, ifthe user has triggered the transition to sitting, yet does not wish tosit, he or she can switch back to the standing state based on theslowing or reversal of the thigh tilt in the sagittal plane.Specifically, the user can slow or reverse the transition from thestanding to the sitting state with his or her arms, via his or herstability aid. If the sagittal thigh tilt velocity (of either or boththighs) falls below a given threshold, the exoskeleton can re-enter thestanding state. Further, the exoskeleton can check the sagittal planethigh tilt (of either or both thighs), and based on the thigh tilt, onlyallow a return to the standing state if the thigh tilt is less than somepredetermined threshold (e.g., to ensure the user is more closelyaligned with the vertical than the horizontal prior to returning to thestanding state).

As shown in FIG. 11, the exoskeleton controller can also consist of atleast a sitting state, a pre-standing state, and a standing state. In apreferred embodiment, the exoskeleton cannot transition directly fromthe sitting state to the standing state, but rather must transition fromsitting to standing through the pre-standing state. The user must meetcertain configuration thresholds to enter the pre-standing state fromthe sitting state. These configuration thresholds can be based onachieving knee flexion thresholds, hip flexion thresholds, or both. Inone embodiment, both knees must be flexed beyond a predeterminedthreshold as a condition to enter pre-standing. In another embodiment,both hips must be flexed beyond a predetermined threshold as a conditionto enter pre-standing. In a preferred embodiment, both knees must firstmeet flexion thresholds, followed by both hips meeting a flexionthreshold, in order to enter the pre-standing state. In a preferredembodiment, in the sitting state, the exoskeleton can move eachrespective knee to the predetermined knee flexion angle when triggeredby a change in the sagittal plane thigh tilt of the respective leg. In apreferred embodiment, entering the pre-standing state generatesvibratory feedback to the user, which informs the user that theexoskeleton is in the pre-standing state. The vibratory feedbackcontinues until the user moves the exoskeleton out of the pre-standingconfiguration thresholds (e.g., the hips are extended), or until theexoskeleton transitions from the pre-standing state to the standingstate. A transition from the pre-standing state to the standing statecan be triggered based on a substantial upward rotation of at least onethigh, indicated by a change in sagittal plane thigh tilt, or an angularvelocity of at least one thigh in the sagittal plane, exceeding apredetermined threshold for a predetermined duration of time. Thesechanges in thigh tilt or thigh angular velocity would be caused by theuser pushing against the ground with his or her stability aid.

2.4.4 Transitions Between Walking and Stairs

As depicted in FIG. 11, the exoskeleton controller consists of at leasta standing state and a stair ascent controller, where the stair ascentcontroller consists of at least a step-up state. The transition from thestanding state to the step-up state is triggered based on the frontalplane thigh tilt exceeding a predetermined threshold angle for apredetermined duration of time. In a preferred embodiment, meeting thisfrontal plane tilt condition will generate a vibratory feedback to theuser, until the step-up state is triggered, or until the condition is nolonger met. In addition to frontal plane thigh tilt, the transition fromstanding to the step-up state can be based on a combination of frontalplane and sagittal plane thigh tilt. In one embodiment, the direction offrontal plane thigh tilt can determine which leg enters the step-upstate. In another embodiment, the direction of frontal plane thigh tiltcan determine whether the controller transitions from the standing stateto a step-up state (for stair ascent), or to a step-down state (forstair descent). In one embodiment, the stair ascent controller consistsof at least a step-up state and a step-to state. The step-up stateraises the respective foot to the next stair tread, while the step-tostate raises the user's body and trailing foot to the same stair tread.The final configuration of the step-to state is the standing state (onthe stair tread above the previous stair). The transition from step-upstate to step-to state can be determined based on the sagittal planethigh tilt of at least one thigh exceeding a predetermined threshold. Inone embodiment, once the controller has entered the stair ascent mode,the transition from standing to each subsequent step-up state is basedon the thigh tilt of at least one thigh exceeding a predeterminedthreshold. In one embodiment the thigh tilt can be frontal plane tilt,while in another embodiment the thigh tilt can be sagittal plane tilt.

When in the stair ascent mode, the determination to leave the stairascent mode can be made while in the standing state based on the frontalplane thigh tilt of at least one thigh exceeding a predeterminedthreshold angle for a predetermined duration of time. In a preferredembodiment, exceeding this thigh tilt threshold will generate avibratory feedback to the user. In particular, a pattern of vibratoryfeedback can be used to inform the user that the exoskeleton is nolonger in stair ascent mode.

As depicted in FIG. 11, the exoskeleton controller consists of at leastone standing state and at least one stair descent mode, where the stairdescent controller consists of at least a step-down state. Thedetermination to enter the stair descent mode (i.e., the step-downstate) from the standing state is based on the frontal plane thigh tiltof at least one thigh exceeding a predetermined threshold angle for apredetermined duration of time. The determination to enter stair descentcan also be based on a combination of frontal and sagittal plane thightilts. In a preferred embodiment, the exoskeleton will generatevibratory feedback when these tilt thresholds have been met, until thestep-down state is entered, or until the tilt thresholds are no longermet. Once in stair descent mode, subsequent switching from the standingstate to the step-down state can be based on frontal or sagittal planethigh tilt (without requiring a predetermined period of time, or issuingvibratory feedback). In a preferred embodiment, the subsequenttriggering of the step-down state is based on the sagittal plane thightilt exceeding a predetermined threshold. In one embodiment, the stairdescent controller consists of at least a step-down state and a step-tostate. The step-down state flexes one knee, while lowering one foot tothe next lower stair tread. The step-to state lowers the trailing footto the same stair tread (and thus the step-to state ends in a standingstate on one step below the previous stair tread). In this embodiment,transition from the step-down state to the step-to state can be based onat least one thigh tilt angle.

When in the stair descent mode, the determination to leave the stairdescent mode can be made while in the standing state based on thefrontal plane thigh tilt of at least one thigh exceeding a predeterminedthreshold angle for a predetermined duration of time. In a preferredembodiment, exceeding this thigh tilt threshold will generate avibratory feedback to the user. In particular, a pattern of vibratoryfeedback can be used to inform the user that the exoskeleton is nolonger in stair ascent mode.

In embodiments directed to switching from standing to stair ascent,stair ascent to standing, standing to stair descent, and stair descentto standing, a sustained frontal plane lean to one side (direction one)will switch from standing to stair ascent; a sustained frontal planelean to the opposite side (direction two) will switch from stair ascentto standing; a sustained frontal plane lean in direction two will switchfrom standing to stair descent; and a sustained frontal plane lean indirection one will switch from stair descent to standing. In otherwords, a sustained lean to one side (e.g., the left side) will cause ageneral upward inflection in terrain, while a sustained lean to theopposite side (e.g., the right side) will cause a general downwardinflection in terrain. In this embodiment, the first step will always betaken with a preferred leg (e.g., the right leg). Also, in theseembodiments, vibratory feedback, via transducers, can provide anindication of meeting the condition to switch into the subsequent mode,and additional vibratory feedback can provide confirmation. Once in therespective stair ascent or descent states, proceeding with stair ascentor descent is then based on forward (i.e., sagittal plane) tilt of thethigh.

In some embodiments, the step-up state of the stair ascent mode and thestep-down state of the stair descent mode each consists of twosub-states, which are a trajectory-controlled sub-state and a dampingsub-state. The former bring the swing foot slightly above the next stairtread, while the latter allows the foot to settle on the stair tread,such that the control system need not know the precise stair height. Inthe case of the step-up state, the damping behavior is primarily in theswing leg, while in the case of the step-down state, the dampingbehavior is primarily in the stance leg. In a preferred embodiment, theexoskeleton system can estimate the step height following each step, andadjust the trajectory of the trajectory-controlled sub-state to moreclosely match the step height.

3. FUNCTIONAL ELECTRICAL STIMULATION

The orthosis described above can be supplemented with functionalelectrical stimulation (FES) of the user's muscles (i.e., usingelectrical stimulation to elicit contractions of the user's muscles).The FES can be controlled by the DES to provide as much movement aspossible, with the remaining movement provided by the assistance device.

One methodology for providing the supplemental FES is as follows. First,the DES can be configured to obtain measures of the amount of motortorque required for a given movement without FES. Thereafter, the DEScan utilize this measurement to estimate the timing and extent of theFES for a given muscle group. The DES can then increase or decrease theFES for that muscle group on a step by step basis to minimize the amountof torque required by the motor on the assistive device. Such aconfiguration allows a user undergoing rehabilitation to primarily relyon the orthosis during initial stages of rehabilitation and to reducehis dependence on the orthosis over time. Alternatively, in the case ofa paraplegic, the FES can be used to stimulate muscle groups in the legsto cause their use. The resulting benefit would be two-fold. First,improved overall health is provided when the paraplegic user is allowedto bear weight on his legs and the muscles in the legs are caused tofunction, as discussed previously. Second, the amount of power neededfor the orthosis is reduced. That is, as FES stimulates and causes themuscles in the legs to operate over time, more of the work for motioncan be performed by the muscles instead of the orthosis.

A general arrangement of the FES electrodes with respect to the orthosisis illustrated in FIG. 13. FIG. 13 is a schematic illustration forproviding FES to the right thigh of a user using the right thigh segment108R in FIGS. 1-4. Although only right thigh segment 108R is discussedherein, this is solely for ease of explanation. A similar configurationcan be used to provide additional FES with the other segment in orthosis100. To provide FES, the right thigh segment 108R is configured toinclude one or more FES source sites 1102 on the surfaces that will befacing or in contact a right thigh 1104 of the user. The arrangement ofFES source sites 1102 in FIG. 13 is provided for illustrative purposesonly. The FES source sites 1102 are configured to coincide with FESreceive sites 1106 on the right thigh 1104, which then provide FES atelectrodes 1107. Note that in some embodiments, it is not required thatthe FES receive sites 1106 coincide exactly with the placement ofelectrodes 1107 on the right thigh 1104. Rather, the FES receive sites1106 can be configured to generally coincide with the FES source sites1102 and to be in direct or indirect communication with the electrodes1107 placed elsewhere on the right thigh 1104.

In the various embodiments, the size and arrangements of the FES sourcesites 1102, FES receive sites 1106, and the electrodes 1107 can vary inaccordance with the configuration needed for FES and/or for a particularuser. For example, the arrangement of electrodes 1107 can be selectedbased on which muscle groups are to receive FES. Accordingly, particulararrangements can be provided for FES of hamstring or quadriceps musclegroups. Other likely sites for electrode source sites and placement areon the anterior and posterior aspects of the shank segments 106R and106L. However, the various embodiments are not limited in this regardand other locations can be used.

In some embodiments, the FES receive sites 1106 and the electrodes 1107can be separately disposed on the right thigh 1104, via the use ofadhesives or the like. In other embodiments, the FES receive sites 1106and the electrodes 1107 can be disposed on the right thigh 1104 using acovering 1108 worn by the user over the right thigh 1104 and under theuser's clothing 1110. In the various embodiments, the covering 1108 canbe a garment, a splint, or any other type of device or apparel wearableby the user. Such a configuration can be advantageous as it reduces theneed for the user to utilize adhesives or be concerned about properalignment of all the electrode areas.

For example, in some embodiments, wireline connections can be provided.That is, the FES source sites 1102 can be directly wired to the FESreceive sites 1106. In such a wireline configuration, it would not benecessary to include coinciding FES source sites 1102. Rather, wirescould be run from one to the FES source sites 1102 to each of the FESreceive sites 1106. In other wireline embodiments, The FES source sites1102 could include needle-type electrodes which mate with electricalcontacts in the FES receive sites 1106. In such a configuration, theneedle type electrodes would be configured to pierce clothing 1110covering the FES receive sites 1106 and thus transmits current throughthe clothing. However, the various embodiments are not limited towireline methods and can also include wireless FES methods. For example,mutual inductance can be used to transmit the FES current from the FESsource sites 1102 through the user's clothing 1110 to the FES receivesites 1106 and on to electrodes 1107. In such embodiments, the covering1108 can include features that locates the FES receive sites 1106relative to the FES source sites 1102 through the clothing 1110. The FESsource sites 1102 would then contain a primary coil, while the FESreceive sites 1106 contain a secondary coil, such that the FES istransmitted through the clothing without wires. Alternatively, thecovering 1108 could include a separate power supply, an FES signalgenerator, and a transceiver for receiving signals from the orthosis,causing the FES signals to be generated and applied to the user.

4. EXAMPLES

The examples shown here are not intended to limit the variousembodiments. Rather they are presented solely for illustrative purposes.

4.1 Preliminary Evaluation

In a first series of tests, the previously described orthosis andcontroller was implemented on a paraplegic subject in order tosubstantiate the ability of a powered orthosis in accordance with thevarious embodiments to provide gait assistance. Table 3 shows a massbreakdown of the resulting orthosis, showing that a light-weightorthosis was provided.

TABLE 3 Mass Breakdown of Orthosis Mass Component (kg) Mass DistributionJoint Actuation 3.57 30% Thigh Frames 4.08 34% Hip Brace 2.10 17% ShankFrames 1.09  9% Battery 0.68  6% Electronics 0.50  4% Total 12.02 100% 

The subject for the first tests was a 35-year-old male (1.85 m, 73 kg)with a T10 complete injury, 8 years post injury. The evaluationsdescribed herein were conducted within a standard set of parallel bars.For the data presented below, the evaluation protocol was as follows.The subject stood from a wheelchair with footrests removed by issuing a“stand” voice command. Note that the footrests, if not removed, wouldobstruct the subject's ability to bring his feet close to the chair, andtherefore would impede his ability to transition from sitting tostanding. Once comfortable standing, the subject issued either a“left-step” or “right-step” voice command, and subsequently, a “step”voice command to initiate subsequent steps. Once near the end of theparallel bars, the subject issued a “half-step” command, which returnedhim to the standing configuration. The subject then turned in place inthe parallel bars by lifting his weight with his arms and incrementallytwisting around in order to walk in the opposite direction. This processrepeated, typically for four to eight lengths of the parallel bars, atwhich point the subject sat (in his wheelchair, by issuing a “sit” voicecommand), so that data from the walking trial could be recorded.

FIG. 14 shows measured joint angle data for each of the joints, as afunction of time, from 23 right steps and 23 left steps, overlaid ontothe same plot. Note that an approximate one-second delay exists betweeneach right and left step, during which time the subject adjusted hisupper body in preparation for commanding the next step. FIG. 15 showsthe same data shown in FIG. 14, with the delay between steps replacedwith a vertical dashed line (which indicates a discontinuity in time),with the time base replaced with a percent stride base, and with theleft and right joint angles overlaid onto the same plots. In thismanner, the knee and hip joint angles can be qualitatively compared tostandard joint kinematics during walking, which is typically representedas a function of stride. These normal biomechanical trajectories arealso plotted in FIG. 15 as dashed lines. The repeatability of the jointangle data over these 23 strides, and the similarity of such data tonormal biomechanics (particularly with respect to the amplitude of kneeflexion, and the amplitude of hip flexion and extension), indicate thatthe powered orthosis is able to provide appropriate and repeatable gaitassistance to the user during walking. The gait represented by this datais characterized by an average overground walking speed of 0.22 m/s (0.8km/hr or 0.5 mi/hr).

Electrical power consumption was recorded during the walking representedby FIGS. 14 and 15. The electrical power required by theservoamplifiers, corresponding to the data shown in FIG. 15, is shownaveraged over all 46 steps (or 23 strides) in FIG. 16. As shown in FIG.16, there is an average power consumption of approximately 35 W for eachknee actuator (during the active stride), and approximately 22 W foreach hip actuator (during the stride). In addition to requiringelectrical power during right and left steps, the joint actuators alsoused power to maintain joint stiffness in the double support states(i.e., while the subject shifted his weight to prepare for the nextstep). For the 46 step sequence previously described, the totalelectrical power required by each actuator was 27 W on average for eachknee motor and 21 W on average for each hip motor during the swing phaseof gait, and 26 W and 29 W of average power for the knee and hip motors,respectively, during the stance phase of gait. The knee brakesadditionally required on average approximately 7 W of electrical powerduring swing, but did not require any power during stance (i.e., theyare normally locked brakes). Finally, the average electrical powerrequired by the remainder of the distributed embedded system wasmeasured as 7.2 W. The average measured electrical power consumption foreach component and each phase of the walking cycle is summarized inTable 4.

TABLE 4 Orthosis Electrical Power Consumption *Average Power Power PowerDuring Between During Stepping Steps Walking Component (W) (W) (W) SwingKnee Motor 34.8 19.6 27.2 Stance Knee Motor 35.6 16.5 26.1 Swing HipMotor 21.4 19.8 20.6 Stance Hip Motor 23.9 34.0 29.0 EmbeddedElectronics 7.2 7.2 7.2 Swing Knee Brake 13.5 0 6.7 Stance Knee Brake 00 0 Total 136.4 97.1 116.8 *Average power with a one-second pausebetween steps (i.e., steps are being taken during 50% of the time during“walking”)

With a one-second average pause between steps (corresponding to the 0.22m/s walking data represented by FIG. 15), the total electrical powerrequired by the system was 117 W. Recall that the battery pack includedin the powered orthosis prototype described herein is a 680 g lithiumpolymer battery with a 115 W-hr capacity. Based on the walking data ofFIG. 16 and Table 3, the battery would provide approximately one hour ofcontinuous walking between charges. At the previously stated (measured)average overground speed of 0.8 km/hr (0.5 mi/hr), the powered orthosiswould provide a range of approximately 0.8 km (0.5 mi) between batterycharges. Note that the range could be easily increased, if desired,without incurring a significant mass penalty, by increasing the size ofthe battery, which currently constitutes 6% of the system mass (seeTable 3). For example, doubling the size of the battery pack woulddouble the range and result in an overall device mass of 12.7 kg, asopposed to 12 kg, as implemented here.

A digital sound level meter was also used while walking with theorthosis to evaluate noise. The average sound level, as measured onemeter away from the orthosis, was approximately 55±2 dBA (with anambient noise level of 38 dBA).

4.2 Assessing Suitability of the Control System

In a second set of tests, the ability of the above-described system toenable a user to autonomously perform the basic movements associatedwith legged mobility (i.e., sitting, standing, and level walking) wasassessed in trials conducted with a paraplegic subject. The subject wasa 35-year-old male (1.85 m, 73 kg) with a T10 motor and sensory completeinjury (i.e., ASIA A), 9 years post injury. All data presented herecorresponds to walking conducted using a walker as a stability aid. Thedata for these tests is shown in FIG. 17.

FIG. 17 shows joint angles (left and right hip, left and right knee) andstate, as a function of time, for the above-identified the subject. Theability of the powered orthosis and control architecture to provideautonomously commanded sitting, standing, and walking was assessed byhaving the subject autonomously perform a timed-up-and-go (TUG) test.The TUG test is a standard clinical measure for assessing leggedmobility. In this test, the subject starts seated in a chair, and givena start command, stands up, walks forward three meters, turns around inplace, walks back to the starting point, and sits down in the chair. Inorder to assess the ability of the subject to autonomously controlmovements of the orthosis, this test was repeated a number of times,until the subject was comfortable performing the test. Once comfortablewith the task, the subject was asked to repeat the TUG test three times.The set of data that corresponds to the third of these three TUG testsis the data shown in FIG. 17.

As shown in FIG. 17, the data shows the right and left hip and kneejoint angles corresponding to this TUG test, along with thecorresponding states of the FSM. In the sequence, the user starts in thesitting state (S1), after which the system enters the sitting tostanding mode (S5), in which both hips and both knees provide torques tofacilitate joint extension. Following S5, the state history depicts aseries of consecutive steps, followed by a period of standing (S2),during which the subject turned in place, with the aid of the walker.The first series of steps is then followed by a second series, duringwhich the subject returned to the chair. Once at the chair, the subjectagain entered standing mode (S2), allowing the subject to turn in place,prior to returning to a seated position in the chair.

Recall that the threshold for the CoP during walking is function of thestep length. FIG. 18A shows the system state for several steps (ofslightly varying length), as a function of time. FIG. 16B shows theestimated CoP (X_(c)) (solid line) and the CoP switching threshold(X_(ĉ)) (dashed line) for the same steps as in FIG. 18A. FIG. 18C showsthe estimate of step length (X_(h)) for the same steps in FIGS. 18A and18B. As seen in the FIGS. 18A-18C, the CoP threshold (X_(ĉ)) varies withstep length (X_(h)). In general, when the CoP (X_(c)) exceeds thethreshold at the end of the swing phase trajectory, the controller willswitch immediately to the contralateral swing phase (i.e., switchingbetween S8 and S9). If the CoP does not cross the CoP threshold at theend of swing phase, the controller will remain in the respective doublesupport phase (S3 or S4) until the user shifts the CoP to cross the CoPthreshold.

FIGS. 19A, 19B, and 19C presents the sequences of finite statescorresponding to each of the first, second, and third TUG tests,respectively. The subject completed the three tests in 103, 128, and 112s, respectively. The average time to complete the sequence was 114 s,with a standard deviation of 8.6 s (7.5%). The consistency betweentrials (i.e., standard deviation of ±7.5%) indicates that the controlapproach described above appears to provide a repeatable means for thesubject to control the basic movements associated with legged mobility.

4.3 Assessing Impact to Paraplegic

The previously described orthosis prototype and control interface wereimplemented on a single paraplegic subject to characterize itsperformance in terms of the standard TUG test and a Ten Meter Walk Test(TMWT). The subject was a 35 year-old male, 9 years post-injury, 1.85 mtall, and with a body mass of 73 kg. Each of the walking test protocolswas performed three times using a walker for stability and three timesusing forearm crutches for stability. To understand the subject'sphysical exertion using the device, heart rate measurements wererecorded at rest before each test and subsequently recorded 30 secondsafter completion of each test. The subject was also asked to rate hisperceived level of exertion according to the Borg scale.

For comparison, the subject then repeated the tests with his ownlong-leg braces and a walker. Traditional long leg braces are used bothin reciprocal gait and swing-through gait (the latter typically with aspreader bar used to constrain the feet to move together) and thereforethe tests were conducted in both walking patterns with the long legbraces. Heart rate measurements and Borg ratings were similarly taken.

Walking in the powered orthosis with a walker yielded the fastest timesin both the TUG test and the TMWT. Both the long leg braces inswing-through gait and the powered orthosis with forearm crutches wereabout 10% slower in each test. The slowest times were recorded with thelong leg braces in reciprocal gait, which were 66% slower in TUG testingand 35% slower in TMWT testing than the times achieved with the poweredorthosis and walker. The results of the timed walking tests are showngraphically in FIG. 20.

Heart rate data from before and after the tests indicated the smallestuser exertion while walking in the orthosis with forearm crutches, withonly an average 3.9% rise in heart rate during TUG and a 1.2% decreaseduring TMWT. Performing the tests with the orthosis and a walkerrequired slightly more user effort, indicated by an average 10.1%increase during TUG and a 5.4% increase during TMWT. The long leg bracesin swing-through gait required significantly more user exertion,resulting in an average 19.0% increase in heart rate during TUG and16.1% increase during TMWT. The highest level of user exertion was seenduring testing with the long leg braces in reciprocal gait, with anaverage 41.8% increase in heart rate during TUG and an 18.4% increaseduring TMWT. A direct correlation was seen between heart rate increaseand the user's perceived exertion. He assigned a Borg scale score of 9to walking with the orthosis and crutches, 10 to the orthosis andwalker, 13 to the long leg braces with swing-through gait, and 14 to thelong leg braces with reciprocal gait. The Borg RPE scale is provided inTable 5.

TABLE 5 Borg Rating of Perceived Exertion Scale SCORE DESCRIPTION  6 NOEXERTION AT ALL  7  7.5 EXTREMELY LIGHT  8  9* VERY LIGHT 10 11 LIGHT 1213** SOMEWHAT HARD 14 15 HARD (HEAVY) 16 17*** VERY HARD 18 19****EXTREMELY HARD 20 MAXIMAL EXERTIONA “9” corresponds to “very light” exercise. For a healthy user, it islike walking slowly at his or her own pace for some minutes. A “13” onthe scale is “somewhat hard” exercise, but it still feels OK tocontinue. A “17” or “very hard” is very strenuous. A healthy user canstill go on, but he or she really has to push him- or herself. It feelsvery heavy, and the user is very tired. A “19” on the scale is anextremely strenuous exercise level. For most people this is the moststrenuous exercise they have ever experienced.

The heart rate data (in terms of percent of change) and Borg ratingsfrom timed walking tests are shown graphically in FIG. 21. A summary ofthe TUG and TMWT scores, heart rate changes, and Borg ratings isprovided in Table 6.

TABLE 6 Summary of Timed Walking Test Data HEART HEART RATE TMWT RATEWALKING TUG TIME CHANGE TIME CHANGE BORG METHOD (SECONDS) (%) (SECONDS)(%) RATING LL BRACES +  178 ± 14 41.8 ± 17.1 109 ± 7  18.4 ± 5.9 14WALKER (RECIPROCAL) LL BRACES + 118 ± 3 19.0 ± 7.2  89 ± 17 16.1 ± 2.913 WALKER (SWING- THROUGH) POWERED 107 ± 5 10.1 ± 4.6  81 ± 10  5.4 ±9.5 10 ORTHOSIS + WALKER POWERED 120 ± 4 3.9 ± 5.4 89 ± 4   −1.2 ± 10.709 ORTHOSIS + FOREARM CRUTCHESResults are average values from three experiments in each walkingmethod.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

Although the invention has been illustrated and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art upon the reading andunderstanding of this specification and the annexed drawings. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Furthermore, to the extent that the terms “including”,“includes”, “having”, “has”, “with”, or variants thereof are used ineither the detailed description and/or the claims, such terms areintended to be inclusive in a manner similar to the term “comprising.”

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

What is claimed is:
 1. A method of controlling an apparatus comprisingan exoskeleton having a hip segment, at least one lower limb, and aplurality of sensors for generating signals indicating a current motionand a current arrangement of at least the exoskeleton, the at least onelower limb comprising a thigh segment and a shank segment for couplingto a lateral surface of a leg of a user, a first powered jointconfigured for providing motion of the thigh segment relative to the hipsegment, and a second powered joint configured for providing motion ofthe shank segment relative to the thigh segment, at least a portion ofthe plurality of sensors being disposed on the at least one lower limb,the method comprising: receiving the signals from the plurality ofsensors; based on the signals, determining a current state of theexoskeleton; estimating a location of a center of pressure of acombination of the user and the exoskeleton based on the signals andinertial properties of the user; inferring a current intent of the userbased on at least the current state of the exoskeleton and a location ofthe center of pressure relative to at least one reference point for theexoskeleton; determining a next state for the exoskeleton based at leaston the current state and the current intent; and generating controlsignals to cause the exoskeleton to transition to the next state.
 2. Themethod of claim 1, further comprising generating at least one of atactile indicia, a visual indicia, or an audio indicia to providefeedback to the user regarding the next state.
 3. The method of claim 1,wherein the step of determining the next state further comprisesselecting one of a plurality of activity modes and a state in the one ofthe plurality of activity modes.
 4. The method of claim 1, furthercomprising generating functional electrical stimulation (FES) signalsfor the at least one lower limb of the user.
 5. The method of claim 4,wherein the step of generating the control signals further comprises,for each of the first powered joint and the second powered joint:determining a first amount of torque required to transition to the nextstate, monitoring a second amount of torque being generated in responseto the FES signals, and configuring the control signals to cause themovement of the exoskeleton to generate a third amount of torque equalto a difference between the first and the second amounts of torque. 6.The method of claim 1, wherein the inertial properties of the usercomprise a center of mass for each of the segments in the at least onelower limb of the user and a center of mass for a combination of a head,arms, and trunk of the user.
 7. The method of claim 1, wherein thesignals correspond to an angle of the hip segment relative to the thighsegment, an angle of the shank segment relative to the thigh segment,and an angle of the thigh segment relative to a direction of gravity. 8.The method of claim 1, wherein the at least one reference pointcomprises a pre-defined portion of the exoskeleton.
 9. The method ofclaim 1, wherein the at least one reference point comprises a locationportion of the exoskeleton.
 10. A computer-readable medium havingcomputer-readable code stored thereon executable by a computercontrolling an exoskeleton, the exoskeleton having a hip segment, atleast one lower limb, and a plurality of sensors for generating signalsindicating a current motion and a current arrangement of theexoskeleton, the at least one lower limb comprising a thigh segment anda shank segment for coupling to a lateral surface of a leg of a user, afirst powered joint configured for providing motion of the thigh segmentrelative to the hip segment, and a second powered joint configured forproviding motion of the shank segment relative to the thigh segment, atleast a portion of the plurality of sensors being disposed on the atleast one lower limb, the computer-readable code comprising a pluralityof instructions causing the computer to perform steps: receiving thesignals from the plurality of sensors; based on the signals, determininga current state of the exoskeleton; estimating a location of a center ofpressure of a combination of the user and the exoskeleton based on thesignals and inertial properties of the user; inferring a current intentof the user based on at least the current state of the exoskeleton and alocation of the center of pressure relative to at least one referencepoint for the exoskeleton; determining a next state for the exoskeletonbased at least on the current state and the current intent; andgenerating control signals to cause the exoskeleton to transition to thenext state.
 11. The computer-readable medium of claim 10, thecomputer-readable code further comprising instructions for causing thecomputer to generate at least one of a tactile indicia, a visualindicia, or an audio indicia to provide feedback to the user regardingthe next state.
 12. The computer-readable medium of claim 10, whereinthe step of determining the next state further comprises selecting oneof a plurality of activity modes and a state in the one of the pluralityof activity modes.
 13. The computer-readable medium of claim 10, thecomputer-readable code further comprising instructions for causing thecomputer to generate functional electrical stimulation (FES) signals forthe at least one lower limb of the user.
 14. The computer-readablemedium of claim 13, wherein the computer-readable code furthercomprising instructions for causing the computer, for each of the firstpowered joint and the second powered joint: to determine a first amountof torque required to transition to the next state, to monitor a secondamount of torque being generated in response to the FES signals, and toconfigure the control signals to cause movement of the exoskeleton togenerate a third amount of torque equal to a difference between thefirst and the second amounts of torque.
 15. The computer-readable mediumof claim 10, wherein the inertial properties of the user comprise acenter of mass for each of the segments in the at least one lower limbof the user and a center of mass for a combination of a head, arms, andtrunk of the user.
 16. The computer-readable medium of claim 10, whereinthe signals correspond to an angle of the hip segment relative to thethigh segment, an angle of the shank segment relative to the thighsegment, and an angle of the thigh segment relative to a direction ofgravity.
 17. The computer-readable medium of claim 10, wherein the atleast one reference point comprises a pre-defined portion of theexoskeleton.